1. Field of the Invention
The present invention relates to a liquid crystal display apparatus, and also to a method for manufacturing the same.
2. Description of the Related Art
A liquid crystal display apparatus has a pair of substrates which are opposed to each other. A cell gap is maintained to a constant value by spacers, and a liquid crystal is filled between the substrates. FIG. 7 is a section view showing the configuration of a liquid crystal display apparatus 220 of the conventional art. The liquid crystal display apparatus 220 has a color filter side substrate 225 and a TFT (Thin Film Transistor) side substrate 226.
In the color filter side substrate 225, a color filter 202, black masks 204, an counter electrode which is not shown, and the like are arranged on a transparent substrate 208 which is made of glass or the like, and the surface is covered with an orientation film 215. In the TFT side substrate 226, liquid crystal driving elements such as TFT elements, wiring portions 203, an insulating film 207, pixel electrodes which are not shown, and the like are arranged on a transparent substrate 209, and the surface is covered with an orientation film 216.
The liquid crystal display apparatus 220 is produced in the following manner. For example, the color filter side substrate 225 and the TFT side substrate 226 are bonded together to form an empty cell, via dispersed spacers 201 for maintaining the cell gap, and a liquid crystal sealing material 214 into which a spacer 213 for maintaining the cell gap in the periphery of the liquid crystal display apparatus 220 is mixed. A liquid crystal 217 is filled into the empty cell. Then, the filling port is sealed by a sealing agent such as a resin.
The cell gap means the gap G between the color filter side substrate 225 and the TFT side substrate 226 in a pixel region where the pixel electrodes are opposed to the counter electrode, and is determined mainly depending on the diameters of the dispersed spacers 201, and the spacer 213 in the sealing material 214, and the filling and sealing conditions of the liquid crystal 217. The uniformity of the cell gap is closely related to the display quality of the liquid crystal display apparatus 220. When the uniformity of the cell gap is low, there arises problems such as that display unevenness such as brightness unevenness or color unevenness is caused in the display screen.
In a rectangular display region 240 of the liquid crystal display apparatus 220, a large number of pixels in which the respective pixel electrodes are opposed to the counter electrode, and the color filters 202 are formed correspondingly with the pixels. In the display region, in order to prevent light from leaking from adjacent pixels, the black mask 204 which surrounds the color filters 202 of the pixels is formed as required into a lattice-like shape extending over the whole of the display region 240. In a picture frame region 241 surrounding the display region, a frame-like black mask 210 is formed.
The black mask 204, 210 is made of a resin in the same manner as the color filters 202. In order to attain sufficient light shielding properties, therefore, the black masks must be formed so as to be thick. Consequently, a film thickness of the black mask 204, 210 is thicker than that of the color filters 202. As a result, protrusions 205 and 212 are formed in the surface of the orientation film 215 of the color filter side substrate 225.
In the liquid crystal display apparatus 220, the protrusions 205 and 212 are formed by the black masks 204 and 210 in the surface of the color filter side substrate 225 which faces the liquid crystal 217. For example, protrusions caused by the wiring portions 203, the liquid crystal driving elements, and the like may be sometimes formed in the surface of the TFT side substrate 226, so that convex and concave portions are formed in the surfaces of the substrates 225 and 226 which face the liquid crystal.
FIG. 7 shows a state in which a uniform cell gap is formed while the dispersed spacers 201 are not placed on the protrusions 205 and 212 formed by the black masks 204 and 210. However, the dispersed spacers 201 are indefinitely placed because the dispersed spacers are randomly dispersed on the color filter side substrate 225 or the TFT side substrate 226.
FIG. 8 is a section view schematically showing a state where a dispersed spacer 206 is placed on a protrusion 205 of the display region. Since the dispersed spacer 206 is placed on the protrusion 205 formed by the black mask 204 of the color filter side substrate 225, the cell gap which is defined by the dispersed spacer 206 placed on the protrusion 205 is larger than that which is defined by the other dispersed spacers 201 placed on the flat portion, by the dimension equal to the height of the protrusion 205. This difference in the substrate gap causes an uneven cell gap, whereby display unevenness such as brightness unevenness or color unevenness is caused in the display screen.
FIG. 9 is a section view schematically showing a state where a dispersed spacer 211 is placed on the protrusion 212 of the picture frame region 241. In the display region 240, most of area excluding the liquid crystal driving elements and the wiring portions 203 is formed by transparent thin films through which pixel electrode light can be transmitted. By contrast, in the picture frame region 241 surrounding the display region 240, the frame-like black mask 210 is formed in order to prevent light from leaking from the region. In this way, the display region 240 and the picture frame region 241 are different from each other in film structure.
The film thickness of the black mask 210 is thicker than that of the color filters 202. This causes a step to be formed between the display region 240 and the picture frame region 241, and the protrusion 212 to be formed on the face of the orientation film 215 of the color filter side substrate 225 in the picture frame region 241. Therefore, the cell gap which is defined by the dispersed spacers 211 placed on the protrusion 212 of the picture frame region is larger than that which is defined by the spacer 213 in the sealing material 214, and the dispersed spacers 211 push up the cell gap in the periphery of the display region. As a result, an uneven cell gap is formed, and display unevenness such as brightness unevenness or color unevenness is caused in the display screen in the vicinities of the dispersed spacers 211.
In some of conventional art techniques for spacers of a liquid crystal display apparatus, the cell gap in the peripheral portion is adjusted by changing the diameter of the spacer 213 in the sealing material 214. In the case where the dispersed spacers 211 are placed on the protrusion 212 due to, for example, the black mask 210 in the picture frame region 241, however, the dispersed spacers 211 affect the value of the cell gap more dominantly than the spacer 213 in the sealing material 214 as shown in FIG. 9. Even when the diameter of the spacer 213 in the sealing material 214 is changed, therefore, unevenness of the cell gap caused by the dispersed spacers 211 placed in the picture frame region 241 cannot be prevented.
By contrast, in another conventional art technique, it is intended to overcome the problem of an uneven cell gap by reducing the thickness of a film forming protrusions, such as a black mask. However, such a technique has a problem in that the thickness of a film forming protrusions cannot be reduced because of a technical reason such as a method for manufacturing the film forming protrusions, or a reason in display quality such as that sufficient light shielding properties cannot be obtained in the case of a reduced film thickness.
In a further conventional art technique, a method is employed in which a liquid acrylic resin or the like is applied to a substrate by the spin coating method, and the applied thin film is fired to overcoat protrusions, thereby enhancing the flatness of the substrate. However, the method of the conventional art technique has a problem in that an overcoating process must be additionally performed.
In a still further conventional art technique disclosed in Japanese Unexamined Patent Publication JP-A 7-92477 (1995), the difference between the cell gap of a portion where an ITO (Indium-Tin Oxide) film serving as a transparent electrode is formed, and that of a portion where the ITO film is not formed is eliminated by forming a dummy ITO film. In the method, however, the position where the ITO film can be formed, and the thickness of the ITO film are restricted, and hence unevenness of the cell gap caused by small protrusions which are formed by a black mask and the like cannot be improved.
It is an object of the invention to provide a liquid crystal display apparatus of high display quality having a uniform cell gap, and also a method for manufacturing the same.
The invention provides a method for manufacturing a liquid crystal display apparatus in which spacers and a liquid crystal are interposed between a pair of substrates, the method comprising the steps of:
forming a protrusion in a liquid-crystal-facing surface of one of the substrates; and
forming a recess in a region of a liquid-crystal-facing surface of the other of the substrates, the region being opposed to the protrusion.
According to the invention, in the case where a protrusion is formed in the one substrate, a recess is formed in a region of the other substrate which region is opposed to the protrusion, whereby the cell gap is prevented from being pushed up by a spacer placed on the protrusion. Even when the substrates are not flat, the cell gap can be uniformalized. In the liquid crystal display apparatus, therefore, reduction of the display quality due to unevenness of the cell gap can be prevented, thereby improving the display quality.
When the recess is formed in a thin film constituting the other substrate, it is not required to add a process of forming an additional film on the surface of the other substrate, such as an overcoating process, and the manufacturing cost is not increased.
Even in the case where a film for forming the protrusion and another film which constitute the one substrate cannot be thinned because of a technical reason or a reason in display quality, the cell gap can be uniformalized by forming the recess in the other substrate.
Furthermore, in the invention it is preferable that the protrusion is a protrusion which is formed by a black mask.
According to the invention, the protrusion is formed in the one substrate by the black mask which is made thicker than a color filter in order to attain light shielding properties, and the recess is formed in the portion of the other substrate, opposed to the protrusion. Therefore, a spacer placed on the protrusion enters the recess, whereby the cell gap is prevented from being pushed up by the spacer. Accordingly, even when the substrates are not flat, the cell gap can be uniformalized.
The invention provides a method for manufacturing a liquid crystal display apparatus in which spacers and a liquid crystal are interposed between a pair of substrates, the method comprising the steps of:
forming a recess in a liquid-crystal-facing surface of one of the substrates; and
forming a protrusion in a portion of a liquid-crystal-facing surface of the other of the substrates, the portion being opposed to the recess.
According to the invention, in the case where a recess is formed in the one substrate, a protrusion is formed in a liquid crystal layer side portion of the other substrate which opposes to the recess, whereby the cell gap can be uniformalized. In the liquid crystal display apparatus, therefore, reduction of the display quality due to unevenness of the cell gap can be prevented, thereby improving the display quality.
When the protrusion is formed in a thin film constituting the other substrate, it is not required to add a process of forming an additional film on the liquid-crystal-facing surface of the substrate, such as an overcoating process, and the production cost is not increased.
The invention provides a method for manufacturing a liquid crystal display apparatus in which spacers and a liquid crystal are interposed between a pair of substrates, the method comprising the steps of:
forming a recess in a liquid-crystal-facing surface of one of the substrates; and
filling the recess.
According to the invention, in the case where a recess is formed in the one substrate, the liquid-crystal-facing surface of the one substrate is adjusted and flattened so as to fill the recess, whereby the cell gap can be uniformalized. In the liquid crystal display apparatus, therefore, reduction of the display quality due to unevenness of the cell gap can be prevented from occurring, thereby improving the display quality.
When the recess is flattened by a thin film constituting the one substrate, it is not required to add a process of forming an additional film on the liquid-crystal-facing surface of the substrate, such as an overcoating process, and the production cost is not increased.
The invention provides a liquid crystal display apparatus comprising:
a pair of substrates;
spacers; and
a liquid crystal,
the spacers and liquid crystal being interposed between the pair of substrates,
wherein a protrusion is formed in a liquid-crystal-facing surface of one of the substrates, and a recess is formed in a region of a liquid-crystal-facing surface of the other of the substrates, the region being opposed to the protrusion.
According to the invention, in the case where a protrusion is formed in the one substrate, a recess is formed in a region of the other substrate opposed to the protrusion, so that, even when the respective substrates are not flat, the cell gap can be uniformalized. In the liquid crystal display apparatus of the invention, therefore, display unevenness such as brightness unevenness or color unevenness can be prevented from occurring, thereby improving the display quality.
Furthermore, in the invention it is preferable that the protrusion is a protrusion which is formed by a black mask.
According to the invention, the protrusion is formed in the one substrate by the black mask which is made thicker than a color filter in order to attain light shielding properties, and the recess is formed in the portion of the other substrate opposed to the protrusion. Therefore, a spacer placed on the protrusion enters the recess, whereby the cell gap is prevented from being pushed up by the spacer. Accordingly, even when the substrates are not flat, the cell gap can be uniformalized.
The invention provides a liquid crystal display apparatus comprising a pair of substrates; spacers; and a liquid crystal, the spacers and liquid crystal being interposed between the pair of substrates,
wherein a recess is formed in a liquid-crystal-facing surface of one of the substrates, and the recess is filled.
According to the invention, in the case where a recess is formed in the one substrate, the liquid-crystal-facing surface of the one substrate is adjusted and flattened so as to fill the recess, whereby the cell gap can be uniformalized. In the liquid crystal display apparatus, therefore, reduction of the display quality due to unevenness of the cell gap can be prevented from occurring, thereby improving the display quality.
The invention provides a liquid crystal display apparatus comprising: a pair of substrates; spacers; and a liquid crystal, the spacers and liquid crystal being interposed between the pair of substrates,
wherein a protrusion having a height H and a width W1 is formed in a liquid-crystal-layer-facing surface of one of the substrates,
a recess having a depth D and a width W2 is formed in a region of a liquid-crystal-layer-facing surface of the other of the substrates, the region being opposed to the protrusion, and
in the case where the height H of the protrusion is smaller than the depth D of the recess, the width W1 of the protrusion and the width W2 of the recess are selected so that the width W1 is larger than the width W2 of the recess.
According to the invention, in a liquid crystal display apparatus, the one and other substrates are separated from each other by a predetermined gap by the spacers, and bonded together so as to be opposed to each other via the liquid crystal. In this configuration, the protrusion formed in the liquid-crystal-facing surface of the one substrate, and the recess formed in the liquid-crystal-facing surface of the other substrate are placed so as to be opposed to each other. For example, the protrusion is a black mask, and the recess is a contact hole which is formed in an insulating layer by a photolithography technique or the like. In the liquid crystal display apparatus of the invention, the protrusion and the recess are set so that, when the height H of the protrusion is smaller than the depth D of the recess, the width W1 of the protrusion is set to be larger than the width W2 of the recess, whereby the cell gap can be uniformalized. Namely, in the case where several spacers are placed on the protrusion, the width W1 of the protrusion is made larger than the width W2 of the recess, thereby causing spacers on the protrusion to exist in the recess and a region other than the recess. Among spacers placed on the protrusion, spacers existing in the recess do not have a function of restricting the cell gap, but those existing in the region other than the recess restrict the cell gap. Therefore, the effect of pushing up spacers is attained by the protrusion, and the cell gap is prevented from being excessively thinned by the recess. In the liquid-crystal display apparatus, consequently, brightness unevenness is prevented from occurring.
Furthermore, in the invention it is preferable that the protrusion is a protrusion which is formed by a black mask.
According to the invention, the protrusion is formed in the one substrate by the black mask which is made thicker than a color filter in order to attain light shielding properties, and the recess is formed in the portion of the other substrate opposed to the protrusion. Therefore, a spacer placed on the protrusion enters the recess, whereby the cell gap is prevented from being pushed up by the spacer. Even when the substrates are not flat, the cell gap can be uniformalized.
Furthermore, in the invention it is preferable that the protrusion and recess are formed in a picture frame region in a periphery of a display region of the liquid crystal display apparatus.
According to the invention, when the film thickness of a black mask placed in a picture frame region in a periphery of a display region is larger than that of a color filter placed in the display region, for example, the flatness of the liquid-crystal-facing surface of the one substrate is lowered. In the picture frame region also, the relationships between the protrusion and the recess are selected as described above, whereby the cell gap is prevented from being excessively thinned by the recess, so that the cell gap can be uniformalized. In the liquid crystal display apparatus, consequently, brightness unevenness can be prevented.
Furthermore, in the invention it is preferable that the protrusion and recess are formed in a region in a picture frame region and separated from a display region.
According to the invention, the protrusion and recess are formed in a region in a picture frame region and separated from the display region, i.e., in the vicinity of a liquid crystal sealing material. Among spacers placed on the protrusion, spacers existing in the recess in the vicinity of the sealing material do not have a function of restricting the cell gap, but those existing in the region other than the recess and separated from the sealing material restrict the cell gap. Therefore, the cell gap is prevented from being excessively thinned by the recess, so that the cell gap can be uniformalized. In the liquid crystal display apparatus, consequently, brightness unevenness can be prevented.
Furthermore, in the invention it is preferable that the protrusion and recess are formed in a region in a picture frame region and in close proximity to a display region.
According to the invention, the protrusion and recess are formed in a region in a picture frame region and in close proximity to the display region. Among spacers placed on the protrusion, spacers existing in the recess in the vicinity of the display region do not have a function of restricting the cell gap, but those existing in the region other than the recess and separated from the display region restrict the cell gap. Therefore, the cell gap is prevented from being excessively thinned by the recess, so that the cell gap can be uniformalized. In the liquid crystal display apparatus, consequently, brightness unevenness can be prevented.
Furthermore, in the invention it is preferable that a second recess is further formed in a periphery of the recess of the other substrate.
According to the invention, the second recess is disposed in a periphery of the recess which is, for example, a contact hole. In a portion of a contact hole serving as the recess, no restriction due to spacers is imposed on the cell gap, and hence the uniformity of the cell gap is locally lowered so as to produce display unevenness. By contrast, in the invention, the other recess is disposed in a periphery of a contact hole serving as the recess, and the uniformity of the cell gap can be therefore prevented from being locally lowered, whereby brightness unevenness can be prevented.